March 17, 2010

What is Accuracy?

At some point in learning to live with diabetes comes the discovery that the number on the blood glucose meter has range of plus or minus twenty percent. That tends to horrify people.
The FDA is having hearings this week on meter accuracy. Good friend of the blog Ellen Ullman is testifying for patients. Yay Ellen! LY/MI!
Ellen has me thinking about accuracy. My thoughts didn’t fit in a tweet. (I am a wee bit wordy - I know it is a schock) She asked at what cost more accuracy; higher co-pay, bigger meters, more blood, and slower response time, all of the above?

All that begs the question that I am really trying to come to grips with: Would tighter variance standard for meters, +/- 15% or 10% result in better health outcomes? Or are there other issues in the whole of T1 care that present greater opportunities for better care?

Well first off what is better care? Lower A1C? Less BG variance? I think most folks would say well it is both low A1C and less glucose variance. Will a tighter margin of error in meters achieve those results?

I suspect that there are many variables in diabetes that are not with in the 20% margin of our meters. How about carb counting? Consider a bowl of spagetti. Are the sources of my information, portion control and actual consumption within 20%. Is the actual sugar content of a tomato that was used to make the pasta sauce that tight? The blend of wheat in the spaghetti? Did the manufacturer vary the high fructose corn syrup to achieve the brand’s signature taste because the tomatoes weren’t as ripe? Is that food label really that accurate? I have no idea.

How about the impact of my activity? Did the effect of the gym on BG vary? Do habits about getting to the gym?

Is the insulin fresh? Did it get too hot? Is the set working well? Air in the tube? How accurate is the amount of insulin drawn into a needle? How is the stress? What is the weather? How early did I pre-bolus.

Assuming all of that is dead on the money, how often am I testing? Those numbers are a point in time. They have no indication of any change in the direction of BG or the rate of that change at the time. And if those numbers vary from the goal is that variation the result of a bolus issue or a basal issue?

Head ready to explode yet?

Is there anyone on God’s Green earth (and I will grant you there is extra green today ‘cause it is St Pat’s - I don’t thing the green die matters but the beer is another story) who has all this figured out to +/- 20%?

So my two bits are this: Accuracy is promoting better outcomes. In that definition, I wish everything varied less.

I think good (a word that means highly automated, very unobtrusive, dirt simple and probably working though a wireless connection between all diabetes devices) analytical tools that can incorporate the whole scope of life with type 1, including the information from meters, could have a more positive effect on outcomes in living lives’ with type 1 than accuracy range of +/- of 10% vs 20%.

The real magic IHMO is in living lives’ with type 1, not dominating lives with diabetes.

7 comments
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Given the huge number of variables and the amount of guestimation involved in diabetes care, I don't see that 100% meter accuracy would make a significant impact on my life or my control.

I remember the days when we used to pass my blood test strip round the family so they could all voice an opinion as to what colour (and therefore BG level) it matched up to on the pot. The variance was generally pretty large so I guess I'm just used to living with ambiguity from an early age!

Then some nasty lows I did not feel so I used control solution to confirm.

I trust my body more than the technology. But....all things in life don't always "measure up."

This is a very poignant post. You hit the nail on the head in Several places.

We can only rely so much on so many things. It's always going to be about balance. For each of us, that balance will be different. Diabetes is a such an individual disease. One form of management (technology) is not best for all.

Well, as you know, Mr. Bad Shoe....YDMV. ;-)

[wv: effieI've a feeling I heard this from somewhere, an old movie maybe, someone yelling "EFFFFIEEEEEEEEE!"....but again, it's late and I am known for my semi-insaneness at my choosing, so, there's that.]

Good points about all of the variables, but isn't it better to eliminate as many variables as possible?To determine how accurate the meters should be, I suggest they look at how accurate the dosing of insulin is.Look at the lines on the side of a 1/3 cc insulin syringe. Consider the insulin pumps with increments of 0.01 units of insulin.Blood glucose meters should approach this level of accuracy, or something is out of whack.If it's OK for my blood sugar reading to be 30 points off, why should my pump deliver increments of less than half a unit?

I agree with jpnairn -- it is impossible to pin down all of the whacky variables that impact our blood sugar, but improving meter accuracy would help eliminate one of them (or come close to it, anyway). A meter being off by +/- 20% really isn't acceptable...I'm sure meter inaccuracy has been the cause of a few "unexplained" lows or strangely persistent highs in my diabetes lifetime.

That said, I think your post is should be read by doctors, insurers, general public, etc., who place blame on people with diabetes for not "being in control" or "not being compliant" or whatever BS judgment they'd like to toss out. How in the heck are we supposed to control the infinite? We can only do our best to shoot at a moving target and hope that we hit it most of the time.

I want significantly improved accuracy for all meters for all persons with diabetes.

It is not only the 20% inaccuracy that is permitted which if find UNacceptable, but perhaps even more so that it only has to be within that 20% above 75 mg/dl 95% of the time - NINETY-FIVE PERCENT OF THE TIME. The other 5% are considered "outliers" without explanation. To hear some in industry or academia discuss it, it felt to me as if outliers are considered nothing more than dots outside of the Clarke Error Grid A/B Zone. But I view the very same dots as flashing warning signs with alarms going off - CAUTION - because of the potential human consequences that may result from that # on the meter.

Some of us are very in tune with our bodies or our children's bodies and know enough not to dose based on a reading that seems so far beyond what we think may really be going on in the body. NOT every person with diabetes, and not every caregiver of a loved one with diabetes, has that intuition, or perhaps has ever had the education to know not to dose without checking again. Many of us are fortunate to have extra test strips to use when we question a number on a meter that doesn't seem congruent with the situation. Some people barely can afford a single test strip let alone 2-3 extra to figure out what the approximate bg value is. So what happens to the 2 yr old whose parents are underinsured, less well educated, or given the cheapest and least accurate meter on the market and the meter says, for example, 350 mg/dl prior to a meal and they give a whopping dose of insulin to correct for the 350 that had they rechecked would have discovered bg was closer to 120 mg/dl? Every single outlier is a potential disaster. It only took the memory of one seizure requiring glucagon injection in my toddler in 1989 or 1990 and the thought of how many have occurred and how many in the future may occur due to meter inaccuracy and excused outliers - to know I needed to stand up before FDA/CDRH and plead for the need for increased accuracy and the ability to compare meters based on performance accuracy. We need to eliminate every possible variable that we can in our daily journey of the diabetes roller coaster ride and tightrope walk. AND we are calibrating our CGMs based on these meters that require less than adequate precision and accuracy - what if your calibration is based on an outlier?